The present invention relates to a fluid lubrication bearing device and a method of manufacturing the same.
A fluid lubrication bearing device supports a shaft member by means of a lubricating film of a fluid generated in a radial bearing gap. Due to its high rotation accuracy, high rotating speed, low cost, and quietness, a bearing device of this type is used in a small motor, for example, a spindle motor for a magnetic disc device, such as an HDD, an optical disc device, such as a CD-ROM, a CD-R/RW, or a DVD-ROM/RAM, a magneto-optical disc device, such as an MD, or an MO, a polygon scanner motor for a laser beam printer (LBP), or a fan motor.
Fluid lubrication bearings of this type are roughly classified into hydrodynamic bearings equipped with a hydrodynamic pressure generating means for generating hydrodynamic pressure in a lubricating oil in a bearing gap, and so-called cylindrical bearings (whose bearing surface is of a perfectly circular configuration) equipped with no hydrodynamic pressure generating means.
For example, in a fluid lubrication bearing device incorporated into the spindle motor of a disc drive device, such as an HDD, there are provided a radial bearing portion supporting a shaft member rotatably in the radial direction in a non-contact manner, and a thrust bearing portion supporting the shaft member rotatably in the thrust direction in a non-contact manner. As the radial bearing portion, there is used a bearing (hydrodynamic bearing) formed by hydrodynamic pressure generating grooves (hydrodynamic pressure grooves) provided on the inner peripheral surface of a bearing sleeve or on the outer peripheral surface of the shaft member. As the thrust bearing portion, there are used, for example, hydrodynamic bearings formed by hydrodynamic pressure grooves provided on both end surfaces of a flange portion of the shaft member or on surfaces opposed thereto (see, for example, JP 2002-61641 A). In some cases, there is used, as a thrust bearing portion, a bearing (a so-called pivot bearing) which supports one end surface of a shaft member in a contact manner by a thrust member (see, for example, JP 11-191943 A).
A fluid lubrication bearing device of this type is composed of a housing, a bearing sleeve, a shaft member, etc., and efforts are being made to enhance the machining precision and assembly precision for each component to secure the high bearing performance as required due to the increasingly improved performance of information apparatuses. On the other hand, with the tendency toward a reduction in the price of information apparatuses, the demand for a reduction in the cost of a fluid lubrication bearing device of this type is becoming more and more strict.